Systems that require very high bandwidth any-to-any connectivity among a set of modules typically use an orthogonal mid-plane configuration. In this configuration, a set of cards are plugged into the front side of the mid-plane in vertical configuration and another set of cards are plugged into the rear side of the mid-plane in horizontal configuration. This layout enables each front card to be directly connected to each rear card, and makes it possible to eliminate the use of PCB signal traces on the mid-plane to carry high speed signals.
However, the orthogonal configuration also creates a cooling challenge, especially in applications where front-to-back cooling is required. Vertical cards can be cooled using conventional cooling mechanisms with front air intake and rear air exhaust, but cooling the horizontal cards while maintaining overall front-to-back air flow is challenging.
If front-to-back cooling is not required, the horizontal card cage can be cooled using side-to-side air flow. However, many rack mount environments require front-to-back air cooling. One solution has been to divert air taken from a front intake to the back and run it up in a column next to the horizontal cards. Such a mechanism typically uses a set of fans or blowers to create the air pressure across the horizontal cards. However, the amount of air flow that is provided in such a system is typically limited due the number of turns in the air path. Also, the placement of one or two fan blades along the sides of the horizontal cards can severely limit the PCB area and panel surface that is available.